1. Field
The present embodiment relates to an image data recording/playback system.
2. Description of the Related Art
For example, a hard disc recorder, which records by storing image data supplied from the outside, such as a digital broadcast signal, etc., encoded in an MPEG2 format, in a hard disc drive (HDD) device, digital video disc (DVD) device, etc., as well as playing back (decoding) and outputting the stored image data, and more specifically, to an image data recording/playback device to which a transcoder is added, which carries out encoding and decoding in an H.264 format capable of encoding with higher efficiency than that of the MPEG2 format.
In a digital broadcast, a broadcast signal is encoded in the MPEG2 format. In addition, as performance improves in a storage device, such as a HDD device, DVD device, etc., an image data recording/playback system is becoming more popular for household use, which records by storing encoded image data in a storage device, as well as decoding and playing it back. The number of products of such an image data recording/playback system for personal use is extensive; however, they are required to be inexpensive, and therefore, their essential parts are incorporated into an LSI to reduce cost. As a result, the main circuits of an image data recording/playback system are implemented by using a standard LSI for a decoder of the MPEG2 format. Generally, a broadcast signal is processed after being divided into picture data and audio data; however, a description is given here on the assumption that image data includes picture data and audio data and image data processing includes picture data processing and audio data processing.
The standard LSI for a decoder currently in use is capable of realizing a function of decoding and playing back MPEG2 image data, an interface function with a storage device, such as a HDD device etc., a function of generating video signals, etc., as well as a chasing playback function for playing back image data being recorded from the beginning, a simultaneous recording/playback function for storing other image data supplied from the outside when playing back image data stored in a storage device, etc.
FIG. 1A is a diagram explaining the operation at the time of the chasing playback function in a system in which MPEG2 image data is stored in a storage device using a standard LSI for an MPEG2 decoder and FIG. 1B is a diagram explaining the operation at the time of the simultaneous recording/playback function.
As shown in FIG. 1A, an operation is carried out by a user in order to instruct chasing processing during the period of recording of MPEG2 image data. In accordance with this, the MPEG2 decoder reads the already recorded MPEG2 image data from the storage device, plays it back, and converts it into an output signal while continuing to record the MPEG2 image data.
As shown in FIG. 1B, an operation is carried out by a user in order to simultaneously record/playback in which MPEG2 image data input during playback of MPEG2 image data being recorded. In accordance with this, the MPEG2 decoder stores new MPEG2 image data in the storage device while continuing playback of MPEG2 image data.
On the other hand, a new encoding format is being considered, which can play back image data of higher quality having a higher compression rate than MPEG2, for example, the H.264 format. By encoding using this format, it is possible to encode the same image with a smaller amount of data and as a result, a longer recording can be stored when the storage capacity of the storage device is the same. Because of this, a new encoding format is being planned; however, the broadcast signal is encoded into the MPEG2 format and there is a problem that an LSI that carries out the processing by the new encoding format has a large-scaled circuit and is expensive. In addition, as described above, the standard LSI for an MPEG2 decoder is widely used and the standard LSI for an MPEG2 decoder is comparatively less expensive. In order to realize an image data recording/playback system that stores image data encoded in a format with a high efficiency at a low cost, an image data recording/playback system having a basic configuration as shown in FIG. 2 is being considered.
The image data recording/playback system shown in FIG. 2 has an MPEG2 decoder 1, an H.264 transcoder 2 that carries out encoding and decoding by the H.264 format, a storage device 3, such as a HDD device, DVD device, etc., and a CPU 4 that controls the system. There may be a case where MPEG2 decoder 1 has the function of CPU 4. The MPEG2 decoder 1 is configured by a standard LSI. An input image signal supplied from outside to MPEG2 decoder 1 is a digital broadcast signal or a digital image signal supplied from other digital image equipment, and it is MPEG2 image data encoded in the MPEG2 format. The H.264 transcoder 2 employs a semi-duplex system in which the H.264 encoding function and the H.264 decoding function do not operate at the same time taking into consideration the realization thereof of low cost.
When recording input image data, MPEG2 decoder 1 supplies input image data to H.264 transcoder 2. H.264 transcoder 2, after playing back the input image data using the MPEG2 decoding function, encodes the H.264 image data using the H.264 encoding function and outputs the H.264 image data to MPEG2 decoder 1. MPEG2 decoder 1 stores the H.264 image data supplied from H.264 transcoder 2 in storage device 3. When playing back the recorded image data, MPEG2 decoder 1 reads the H.264 image data from storage device 3 and supplies it to H.264 transcoder 2. H.264 transcoder 2 plays back the H.264 image data using the H.264 decoding function and outputs the played-back image data to MPEG2 decoder 1. MPEG2 decoder 1 converts the played-back image data supplied from H.264 transcoder 2 into an analog video output or a digital HD video output (HDMI) and outputs it.
As described above, the image data recording/playback system in FIG. 2 only stores the H.264 image data with a high compression rate in storage device 3. Due to this, it is possible to effectively use the storage capacity of storage device 3 and to record for a longer period of time.
As described above, the system in FIG. 2, in which transcoder 2 of the semi-duplex system is added to MPEG2 decoder 1, will not bring about a problem when carrying out normal recording and playback operations. However, as described above, the standard LSI for an MPEG2 decoder can realize the chasing playback function, the simultaneous recording/playback function, etc., and a system, in which MPEG2 image data is stored in a storage device using the standard LSI, has in general the chasing playback function, the simultaneous recording/playback function, etc. Because of this, the image data recording/playback system that stores H.264 image data in the storage device shown in FIG. 2 is also required to realize the same functions.
However, as shown in FIG. 1A and FIG. 1B, when the chasing playback or the simultaneous recording/playback are carried out, it is necessary to carry out recording and playback at the same time. In the system in FIG. 2, the H.264 image data is input/output to/from storage device 3, and therefore, it is necessary to carry out the recording and playback of H.264 image data at the same time, however, because H.264 transcoder 2 employs the semi-duplex system, it is not possible to carry out the processing at the same time. Because of this, with the system in FIG. 2, there is a problem in that the chasing playback function or the simultaneous recording/playback function cannot be realized.
As described above, a system, in which a transcoder of the semi-duplex system employing a second encoding format the compression rate of which is higher than that of a first encoding format is added, has a problem in that it is not possible to carry out recording and playback at the same time because the transcoder employs the semi-duplex system.